The present invention relates to room air treatment systems. Such systems typically comprise a cabinet in which are mounted a large particle prefilter, a fine filter and a fan which pulls air through the filters and blows it back into the room. Such systems are relatively inefficient, noisy and generally not effective against chemical contaminants in the air.
Some systems incorporate carbon filters in order to eliminate odorous and chemical contamination. The carbon is often bonded to some type of fibrous material.
Some systems use carbon filters in which carbon granules are contained in a honeycomb support matrix. The honeycomb matrix comprises a plurality of cells, each of which contains carbon granules. It is difficult to pack each cell full and consequently, there is an air space above the carbon. This leads to air passing over the carbon rather than through it.
One prior art system draws air into a blower through a large particle prefilter and a carbon filter, and then forces it out through a fine particle high efficiency particulate air (HEPA) filter and out into the room.sup.1 However, as the HEPA filter accumulates aerosol particles and odor bearing entrained particles, the associated gases eventually are carried off the filter and are conveyed into the room. FNT .sup.1 U.S. Pat. No. 3,812,370 to Fred G. LaViolette, issued May 21, 1974 and entitled "Low Cost Portable Room Air Cleaner."
Indeed, one serious drawback to many room air treatment system is knowing when to change the filters. Dirty filters can become breeding grounds for problems. A satisfactory control system for warning a user to change filters would be desirable.